Aspects of the disclosure relate to the suppression of signal distortion in RF communication systems, for example, wireless handsets.
A RF receiver mixes an incoming signal thereby changing its carrier frequency. In a heterodyne receiver, the mixer changes the incoming signal's carrier frequency to an intermediate frequency. In a direct conversion RF receiver, otherwise called a zero IF RF receiver, the mixer changes the incoming signal's carrier frequency to a frequency of zero.
A given mixer may generate distortion components, including a distortion referred to as the “second order IM2 distortion.” This distortion is at a relatively low frequency, and thus generally does not have a large impact on the signal-to-noise ratio of a mixed signal in a heterodyne receiver. In contrast, in the zero IF RF receiver, the second order IM2 distortion more closely coincides with the down converted (mixed) signal. The IM2 distortion is at a low frequency, and the mixed signal with a carrier frequency of zero is also at a low frequency. Therefore, with the zero IF RF receiver, the second order IM2 distortion has much more of an impact on the mixed signal's signal-to-noise ratio.